The ever increasing demand for additional bandwidth in communication systems has put further focus on exploiting all available media, e.g. indoor cabling. Data transmission at short distances is now a topic of great interest, as small cells are used more and more to provide wireless coverage indoors and in well-defined regions with high bandwidth requirements, such as a university campus. Therefore, copper cables, such as twisted pair, are receiving renewed interest. Improved cables, such as Category 5, 6, 7 and 8 with their more stringent specifications for e.g. crosstalk and insertion loss, considerably extend the exploitable bandwidth.
In order to ensure reliable operation according to current and future technical standards and regulations, monitoring and diagnostics of deployed networks become more and more important. Hence it is beneficial for a network administrator to know line properties, such as quality, length and type of termination of the respective line segments, especially during the deployment of the telecommunication system.
Electrically conducting lines of a communication system can be examined with Time Domain Reflectometry, TDR, which is a measurement technique used to determine transmit characteristics through the reflections when an electrical impulse, or fast step, is propagated down a transmission line. Frequency Domain Reflectometry, FDR, is the frequency domain counterpart of TDR. Both are related through Fourier transformation. TDR/FDR can be used for determining the distance to the far-end of the line and/or for fault detection, fault localization and performance estimation. However, TDR as applied today is associated with some limitations. For instance, determining properties of electrically conductive lines, such as their length, termination and respective electrical parameters, is a challenging task, mainly due to the computational burden and difficulty in obtaining sufficient accuracy in the end result. Noise can be a significant source of error when measuring small variations in impedance. Attempts to reduce the effects of noise by performing signal averaging can be very demanding computationally and sometimes the measurement time must be short in order to minimize disturbance caused by the measurement signal. The type of line termination and its associated properties, such as its impedance, can be particularly difficult to determine due to difficulties in differentiating between different types of line termination.
TDR as applied today is based on the principle that each received signal results from a reflection of the original test signal at the interface between the test device and the line that is tested and reflections from all line terminations, segment changes, faults, etc.
One of the neglected limitations associated with TDR is the effect of numerous tiny imperfections resulting in small reflections (note that no two lines are exactly alike). Those multiple reflections blur the reflected signal and are perceived as an additional noise source. However, when an electrically conducting line is measured using narrowband signals, the measurement's limited time-resolution makes the imperfections undetectable.
The TDR peak is typically wide, attenuated and includes energy also from other reflection points besides the major reflection. The magnitude of an associated reflection coefficient is then difficult to estimate accurately. Phase distortion due to dispersion of the electrically conductive line also adversely affects precision of the estimate. This is also a significantly contributing factor for uncertainty in the calculation of the reflection coefficient and/or interesting features of the electrically conductive line. An uncertainty of the estimates arises also from the imperfect line equipment setup and calibration.
A further source of uncertainty arises from the question of whether the termination can be regarded as a lumped element or a distributed termination. A trace can be formed from received reflections from impedance discontinuities. A trace of reflections is a function representing magnitudes of reflections over a period of time. For characteristically or almost characteristically terminated lines, TDR as applied today often fails to detect the line end, which means that the line will appear to be infinitely long. When the line end is open or short-circuited, the TDR trace continues undisrupted except a visible, distinct reflection at the end of the line. It is currently quite challenging to determine if the continuation of the TDR trace after the distinct reflection is due to internal reflections or due to following line segments.
Thus, there is a need in the art for new line estimation methods and devices that are able to determine line termination and determine line termination characteristics.